Fuel composition

ABSTRACT

A fuel oil composition comprising: (A) a major proportion of a middle distillate petroleum fuel having a wax content of less than 2 wt % at 10° C. below the wax appearance point of the fuel, and either: (i) a final boiling point of greater than 355° C. and either a (90-20%) distillation range of greater than 115 ° C. or a (FBP-90%) distillation range of 30° C. or greater; or (ii) a final boiling point of greater than 360° C. and either a (90-20%) distillation range of greater than 110° C. or a (FBP-90%) distillation range of 25° C. or greater; or (iii) a final boiling point of greater than 370° C. and either a (90-20%) distillation range of greater than 100° C. or a (FBP-90%) distillation range of 250° C. or greater), and (B) a minor proportion of an additive comprising: (B1) an ethylene-unsaturated ester copolymer flow improver, other than an ethylene-vinyl acetate bipolymer, the flow improver having an unsaturated ester content of greater than 10 mole %; and, optionally, (B2) an ethylene-unsaturated ester copolymer that is different from (B1).

This application is a 371 of PCT/EP96/01728 filed on Apr. 23, 1996.

This invention relates to fuel compositions.

BACKGROUND OF THE INVENTION

Petroleum distillates such as diesel oil or fuel oil contain, dependingon their sources and distillation conditions, normal paraffins which incertain latitudes in winter precipitate as waxy crystals at lowtemperatures. As the temperature in the oil fails, the crystals tend togrow into large platelets and their presence eventually increases theviscosity of the fuel to an extent that it can no longer be poured (pourpoint). In the 1960's, ethylene/vinyl acetate copolymers (EVA), such asdescribed in U.S. Pat. No. 3,093,623 and U.S. Pat. No. 3,048,479 wereused commercially as additives for lowering the pour point of the oilsat fairly low temperatures. The pour point is however some degrees belowthe temperature at which the wax crystals begin to appear (known as thecloud point) and so the fuel will still pour despite the presence ofsome wax crystals.

It was also found that depression of the pour point was not the onlydecisive factor for the winter time handling of paraffin-containingpetroleum distillates. Specifically, it was found that at temperaturesbetween the cloud point and the pour point, large wax crystals couldsometimes form which could prevent the oil passing through filtersdespite its ability to pour. To measure this filter plugging tendency,the Cold Filter Plugging Point (CFPP) test was developed and became aEuropean standard. It was found that petroleum middle distillates couldmore readily be conveyed through pumps and filters, with less danger ofblockages occurring due to precipitates of waxy paraffin crystals, byuse of suitable additives to hold the crystal growth within such limitsthat only small crystals precipitated. Such suitable additives were alsobased on ethylene/vinyl acetate copolymers. These show the surprisingeffect of not only depressing the pour point, but also substantiallyrestricting the growth in size of the paraffin crystals. This is due tothe EVA having a low degree of branching of 6 or fewer methyl sidechains, thereby giving an improvement in the CFPP performance of theoil.

However, it has now been found that, in certain fuels, ethylene-vinylacetate copolymers give unacceptable variation in CFPP results due torandomly occurring aspiration anomalies in carrying out the test. Thus,the refiner may not be able to reliably treat the fuel or may have totreat the fuel with higher additive concentrations than should benecessary.

More specifically, fuel oil compositions being middle distillatepetroleum-based fuel oils treated with ethylene-vinyl acetate flowimprovers are typically produced to meet a specified target for CFPPperformance (referred to herein as the `CFPP Specification`), which isdetermined by measurement in the CFPP test. Aspiration anomalies giverise to variable results in the test, making the task of accuratelydetermining CFPP performance difficult and giving rise to doubts overwhether the fuel oil composition meets its CFPP Specification. Theseaspiration anomalies have been observed particularly when untreated fueloils having the following characteristics are used as the base fuel insuch compositions;

a wax content of less than 2 wt % at 10° C. below wax appearancetemperature, and either

(i) a final boiling point of greater than 355° C.; and either a (90-20%)distillation range of greater than 115° C. or a (FBP-90%) distillationrange of 30° C. or greater, or

(ii) a final boiling point of greater than 360° C.; and either a(90-20%) distillation range of greater than 110° C. or a (FBP-90%)distillation range of 25° C. or greater, or

(iii) a final boiling point of greater than 370° C.; and either a(90-20%) distillation range of greater than 100° C. or a (FBP-90%)distillation range of 25° C. or greater,

all temperatures being measured in accordance with ASTM D-86.

It has been found that this aspiration problem may be overcome by theaddition of higher levels of the ethylene-vinyl acetate copolymers inthese critical base fuel oils, to the point where the incidence ofaspirations becomes negligible. However, this results in the use ofexcessive amounts of the copolymers and does not represent an economicalway of obtaining fuel oil compositions reliably meeting their CFPPSpecification.

It has now been discovered that treating the above-defined critical basefuel oils with certain other ethylene vinyl ester copolymer flowimprovers leads to specific fuel oil compositions which are less proneto aspirations and which have comparable or even improved CFPP potency.As a result, the fuel producer may produce fuels reliably meeting therequired CFPP Specification whilst using substantially less flowimprover, so obtaining the desired fuel oil compositions moreeconomically and consistently.

SUMMARY OF THE INVENTION

Thus, a first aspect of the invention is a fuel oil compositioncomprising

(A) a major proportion of a middle distillate petroleum-based fuel oilhaving a wax content of less than 2 wt % at 10° C. below the waxappearance temperature of the fuel, and either

(i) a final boiling point of greater than 355° C.; and either a (90-20%)distillation range of greater than 115° C. or a (FBP-90%) distillationrange of 30° C. or greater; or

(ii) a final boiling point of greater than 360° C.; and either a(90-20%) distillation range of greater than 110° C. or a (FBP-90%)distillation range of 25° C. or greater; or

(iii) a final boiling point of greater than 370° C.; and either a(90-20%) distillation range of greater than 100° C. or a (FBP-90%)distillation range of 250° C. or greater,

all temperatures being measured in accordance with ASTM D-86, and

(B) a minor proportion of an additive comprising

(B1) an ethylene-unsaturated ester copolymer flow improver, other thanan ethylene-vinyl acetate bipolymer, the flow improver having anunsaturated ester content of greater than 10 mole %; and, optionally,

(B2) an ethylene-unsaturated ester copolymer that is different from(B1).

A second aspect of the invention is use of additive (B), as definedabove, in fuel oil (A), as defined above, to provide a fuel oilcomposition reliably meeting its required CFPP specification.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Features of the invention will now be discussed in further detail asfollows:

ADDITIVE

(B1): Ethylene unsaturated ester copolymer flow improvers have apolymethylene backbone divided into segments by hydrocarbyl side chainsinterrupted by one or more oxygen atoms and/or carbonyl groups.

More especially, the copolymer may comprise an ethylene copolymerhaving, in addition to units derived from ethylene, units of the formula

    --CR.sup.5 R.sup.6 --CHR.sup.7 --

wherein R⁶ represents hydrogen or a methyl group; R⁵ represents a--OOCR⁸ or --COOR⁸ group wherein R⁸ represents hydrogen or a C₁ to C₂₈,preferably C₁ to C₁₆, more preferably C₁, to C₉, straight or branchedchain alkyl group; most preferably C₅ -C₂₈, and R⁷ represents hydrogenor a --COOR⁸ or --OOCR⁸ group, provided that the copolymer is not anethylene-vinyl acetate bipolymer.

These may comprise a copolymer of ethylene with an ethylenicallyunsaturated ester, or derivatives thereof. An example is a copolymer ofethylene with an ester of an unsaturated carboxylic acid such asethylene - acrylates (e.g. ethylene -2ethylhexylacrylate), but the esteris preferably one of an unsaturated alcohol with a saturated carboxylicacid such as described in GB-A-1,263,152. An ethylene/vinyl estercopolymer is advantageous; ethylene vinyl propionate, ethylene-vinylhexanoate, ethylene 2-ethylhexanoate, or ethylene-vinyl octanoatecopolymer is preferred. Preferably, the copolymers contain from greaterthan 10 to 25 such as less than 25, e.g. up to 20 such as 11 to 20, mole% of the unsaturated ester, more preferably from greater than 10 to 15such as 11 to 15 mole % unsaturated ester. Preferably, number averagemolecular weight, as measured by vapour phase osmometry, of thecopolymer is 1,000 to 10,000, more preferably 1,000 to 5,000. Ifdesired, the copolymers may be derived from additional comonomers, e.g.they may be terpolymers or tetrapolymers or higher polymers, for examplewhere the additional comonomer is isobutylene or diisobutylene oranother ester giving rise to different units of the above formula andwherein the above-mentioned mole %'s of ester relate to total ester. Themole % of unsaturated ester is believed to help control the incidence ofaspirations observed with the critical oils.

Also, the copolymers may include small proportions of chain transferagents and/or molecular weight modifiers (e.g. acetaldehyde orpropionaldehyde) that may be used in the polymerisation process to makethe copolymer.

The copolymers may be made by direct polymerisation of comonomers. Suchcopolymers may also be made by transesterification, or by hydrolysis andreesterification, of an ethylene unsaturated ester copolymer to give adifferent ethylene unsaturated ester copolymer. For example, ethylenevinyl hexanoate and ethylene vinyl octanoate copolymers may be made inthis way, e.g. from an ethylene vinyl acetate copolymer.

The copolymers may, for example, have 15 or fewer, preferably 10 orfewer, more preferably 6 or fewer, most preferably 2 to 5, methylterminating side branches per 100 methylene groups, as measured bynuclear magnetic resonance, other than methyl groups on a comonomerester and other than terminal methyl groups.

The copolymers may have a polydispersity of 1 to 6 preferably 2 to 4,polydispersity being the ratio of weight average molecular weight tonumber average molecular weight both as measured by Gel PermeationChromatography using polystyrene standards.

Preferred examples of terpolymers are ethylene terpolymers having, inaddition to units derived from ethylene, units of the formula ##STR1##and units of the formula ##STR2## wherein R¹ and R², which may be thesame or different, each represent H or methyl, R³ represents an alkylgroup having up to 4 carbon atoms, and R⁴ represents a linear orbranched alkyl group having from 3 to 15 carbon atoms, R³ and R⁴ beingdifferent. Preferably, R⁴ represents a branched chain alkyl group havingfrom 8 to 15 carbon atoms, which may or may not be a tertiary alkylgroup, or represents a branched chain alkyl group having at most 7carbon atoms.

(B2): The optional ethylene-unsaturated ester polymers under (B2) may bedefined as under (B1), but without the mole % unsaturated esterrestriction and including ethylene-vinyl acetate bipolymers. Actually,ethylene-vinyl acetate bipolymers are preferred.

(B2) may comprise more than one polymer, e.g. where one polymer has anunsaturated ester content of 10 to 25 mole % and another polymer has anunsaturated ester content of less than 10 mole % such as 3.5 to 7 mole%.

CO-ADDITIVES

The aforementioned additives may be used in combination with one or morecoadditives including one or more of the following:

Comb Polymers which are discussed in "Comb-Like Polymers. Structure andProperties", N. A. Plate and V. P. Shibaev, J. Poly. Sci. MacromolecularRevs., 8, p 117 to 253 (1974).

Generally, comb polymers consist of molecules in which long chainbranches such as hydrocarbyl branches, optionally interrupted with oneor more oxygen atoms and/or carbonyl groups, having from 6 to 30 such as10 to 30, carbon atoms, are pendant from a polymer backbone, saidbranches being bonded directly or indirectly to the backbone. Examplesof indirect bonding include bonding via interposed atoms or groups,which bonding can include covalent and/or electrovalent bonding such asin a salt. Generally, comb polymers are distinguished by having aminimum molar proportion of units containing such long chain branches.

Advantageously, the comb polymer is a homopolymer having, or a copolymerat least 25 and preferably at least 40, more preferably at least 50,molar per cent of the units of which have, side chains containing atleast 6 such as at least 8, and preferably at least 10, atoms, selectedfrom for example carbon, nitrogen and oxygen, in a linear chain or achain containing a small amount of branching such as a single methylbranch.

Examples of comb polymers are described in EP-A-214,786; EP-A-213,879;EP-A-153,176; EP-A-153,177; EP-A-156,577; EP-A-225,688; WO 91/16407;EP-A-282,342; and WO 93/19106.

Linear Compounds which comprise a compound in which at least onesubstantially linear alkyl group having 10 to 30 carbon atoms isconnected via an optional linking group that may be branched to anon-polymeric residue, such as an organic residue, to provide at leastone linear chain of atoms that includes the carbon atoms of said alkylgroups and one or more non-terminal oxygen, sulphur and/or nitrogenatoms. The linking group may be polymeric.

By "substantially linear" is meant that the alkyl group is preferablystraight chain, but that straight chain alkyl groups having a smalldegree of branching such as in the form of a single methyl group branchmay be used.

Preferably, the compound has at least two of said alkyl groups when thelinear chain may include the carbon atoms of more than one of said alkylgroups. When the compound has at least three of said alkyl groups, theremay be more than one of such linear chains, which chains may overlap.The linear chain or chains may provide part of the linking group betweenany two such alkyl groups in the compound.

The oxygen atom or atoms, if present, are preferably directly interposedbetween carbon atoms in the chain and may, for example, be provided inthe linking group, if present, in the form of a mono- orpoly-oxyalkylene group, said oxyalkylene group preferably having 2 to 4carbon atoms, examples being oxyethylene and oxypropylene.

Examples of linear compounds are described in EP-A-61,895; U.S. Pat. No.4,491,455; JP 2-51477; JP 3-34790; EP-A-1 17,108; EP-A-326,356; andEP-A-356,256.

Polar Compounds

Such compounds comprise an oil-soluble polar nitrogen compound carryingone or more, preferably two or more, hydrocarbyl substituted amino orimino substituents, the hydrocarbyl group(s) being monovalent andcontaining 8 to 40 carbon atoms, which substituent or one or more ofwhich substituents optionally being in the form of a cation derivedtherefrom. The oil-soluble polar nitrogen compound is either ionic ornon-ionic and is capable of acting as a wax crystal growth modifier infuels. Preferably, the hydrocarbyl group is linear or slightly linear,i.e. it may have one short length (1-4 carbon atoms) hydrocarbyl branch.When the substituent is amino, it may carry more than one saidhydrocarbyl group, which may be the same or different.

The term "hydrocarbyl" refers to a group having a carbon atom directlyattached to the rest of the molecule and having a hydrocarbon orpredominantly hydrocarbon character. Examples include hydrocarbongroups, including aliphatic (e.g. alkyl or alkenyl), alicyclic (e.g.cycloalkyl or cycloalkenyl), aromatic, and alicyclicsubstitutedaromatic, and aromatic-substituted aliphatic and alicyclic groups.

Aliphatic groups are advantageously saturated. These groups may containnonhydrocarbon substituents provided their presence does not alter thepredominantly hydrocarbon character of the group. Examples include keto,halo, hydroxy, nitro, cyano, alkoxy and acyl. If the hydrocarbyl groupis substituted, a single (mono) substituent is preferred.

Examples of polar compounds are described in U.S. Pat. No. 4,211,534;EP-A-272,889: U.S. Pat. No. 4,147,520; EP-A-261,957; EP-A-316,108.

FUEL OIL

The fuel oil is obtained in refining crude oil as the fraction betweenthe lighter kerosene and jet fuels fraction and the heavier fuel oilfraction. Examples are kerosene, jet fuels, diesel fuels, heating oils,and heavy fuel oils.

The wax appearance temperature of the fuel is as measured byDifferential Scanning Calorimetry (DSC). Wax appearance temperature is ameasure of the onset of crystallisation and hence the Cloud Point. Thus,a small sample (25 μl) of test fuel is cooled at 2° C./minute from atemperature at least 30° C. above the expected cloud point of the fuel.An exotherm is observed when crystallisation commences in the sample andthe WAT is measured by an extrapolation technique using a MettlerTA2000B differential scanning calorimeter.

The distillation characteristics are as set forth in Designation D-86 ofthe American Society for Testing and Materials (ASTM).

TREAT RATES

The concentration of the additive in the oil may for example in therange of 1 to 5000 ppm of additive (active ingredient) by weight perweight of fuel, for example 10 to 5,000 ppm such as 10 to 2000 ppm(active ingredient) by weight per weight of fuel, preferably 25 to 500ppm, more preferably 50 to 200 ppm, for example 60 to 90 ppm.

The additive or additives should be soluble in the oil to the extent ofat least 1000 ppm by weight per weight of oil at ambient temperature.However, at least some of the additive may come out of solution near thecloud point of the oil in order to modify the wax crystals that form.

CONCENTRATES

Concentrates comprising the additive in admixture with a carrier liquid(e.g. as a solution or a dispersion) are convenient as a means forincorporating the additive into bulk oil such as distillate fuel, whichincorporation may be done by methods known in the art. The concentratesmay also contain other additives as required and preferably contain from3 to 75 wt %, more preferably 3 to 60 wt %, most preferably 10 to 50 wt% of the additives preferably in solution in oil. Examples of carrierliquid are organic solvents including hydrocarbon solvents, for examplepetroleum fractions such as naphtha, kerosene, diesel and heater oil.aromatic hydrocarbons such as aromatic fractions, e.g. those sold underthe `SOLVESSO` tradename; and paraffinic hydrocarbons such as hexane andpentane and isoparaffins. The carrier liquid must, of course, beselected having regard to its compatibility with the additive and withthe fuel.

The additives of the invention may be incorporated into bulk oil byother methods such as those known in the art. If co-additives arerequired, they may be incorporated into the bulk oil at the same time asthe additives of the invention or at a different time.

OTHER CO-ADDITIVES

The additives of the invention may be used singly or as mixtures. Theymay also be used in combination with one or more co-additives such asknown in the art, for example the following: detergents, antioxidants,corrosion inhibitors, dehazers, demulsifiers, metal deactivators,antifoaming agents, cetane improvers, cosolvents, packagecompatibilisers, reodorants, lubricity additives and antistaticadditives.

EXAMPLES

The following examples illustrate the invention.

Materials Used

Additive Components

A1: an ethylene-vinyl acetate copolymer of number average molecularweight 5000 as measured by GPC (Gel Permeation Chromatography) againstpolystyrene standards and containing 13.5% by weight of vinyl acetate.

A2: an ethylene-vinyl acetate copolymer of number average molecularweight 3300 as measured by GPC and containing 36% by weight of vinylacetate.

B: an ethylene-vinyl acetate--vinyl 2-ethyl hexanoate terpolymer, madeby free radical copolymerisation of the comonomers, containing 4.0 mole% vinyl acetate, 11.1 mole % vinyl 2-ethyl hexanoate, balance ethylene,having an Mn of 4,200 (by GPC) and a CH₃ /100 CH₂, not corrected forterminal methyl groups of 4.0, dissolved in a heavy aromatic naphthasolvent at 60% active ingredient dilution.

Formulations (all wt %)

X: 4.5% Al, 59% A2 and the remainder being solvent.

Y: 5% Al, 14.8% A2, 30.1 % B, the remainder being solvent.

Fuels

    ______________________________________                                                             I    II                                                  ______________________________________                                        Cloud Point (° C.)                                                                            -1     -3                                                Wax (mass %) 10° C. below cloud point 1.9 1.9                          D-86 (° C.)                                                            IBP 172 172                                                                   10% 213 204                                                                   20% 231 219                                                                   50% 280 265                                                                   90% 346 340                                                                   95% 359 355                                                                   FBP 371 367                                                                   90%-20% 115 121                                                               FBP-90%  25  27                                                             ______________________________________                                    

Test Method (Cold Filter Plugging Point (CFPP) Test)

The test which is carried out by the procedure described in detail in"Journal of the Institute of Petroleum", Volume 52, Number 510, June1966, pp.173-285, and more recently in European Standard EN 116, isdesigned to correlate with the cold flow of a middle distillate inautomotive diesels.

In brief, a sample of the oil to be tested (40 ml) is cooled in a bathwhich is maintained at about -34° C. to give non-linear cooling at about1° C./min. Periodically (at each one degree centigrade starting fromabove the cloud point), the cooled oil tested for its ability to flowthrough a fine screen in a prescribed time period using a test devicewhich is a pipette to whose lower end is attached an inverted funnelwhich is positioned below the surface of the oil to be tested. Stretchedacross the mouth of the funnel is a 350 mesh screen having an areadefined by a 12 millimeter diameter. The periodic tests are eachinitiated by applying a vacuum to the upper end of the pipette wherebyoil is drawn through the screen up into the pipette to a mark indicating20 ml of oil. After each successful passage, the oil is returnedimmediately to the CFPP tube. The test is repeated with each one degreedrop in temperature until the oil fails to fill the pipette within 60seconds, the temperature at which failure occurs being reported as theCFPP temperature.

Test Procedure

Formulations X and Y were each dissolved in Fuels I and II at specifiedtreat rates and the CFPP measured as described above.

Results

    __________________________________________________________________________    Fuel I                                                                        Treat Rate (ppm)                                                                      75                                                                              100 125 150 175 200 225                                                                              250                                                                              300                                       __________________________________________________________________________      Formulation X -5  -7 -13 (A) -13 (A)  -15                                        -6  -6 -10 (A) -12 -12 (A) -16 -17 -17                                        -6  -6 -13 -14 -16 -18 -18 -16                                                -6  -9 (A) -13 (A) -13 (A) -12 -17 -17 -17                                    -5  -7 -12 (A) -16 -14 -15 -16 -18                                            -5  -6 -13 (A) -15 -15 (A) -15 -15 -15                                        -5  -7                                                                        -6 -11                                                                        -6  -6                                                                     Formulation Y -7 -15 (A) -15 -16  -17                                           -10 (A) -13 -15 -15 -16                                                       -10 (A) -10 -16 -16 -17                                                        -8 -13 -14 -16 -14                                                            -6 -13 (A) -16 -16 -17                                                       -13 -14 -15  -16                                                               -8 (A) -16                                                                   -11 (A) -14                                                                    -9 (A) -15                                                                   100 125                                                                     Additive B alone   -6 -17                                                        -7 -18                                                                       -10 (A) -18                                                                    -8 (A) -18                                                               __________________________________________________________________________    Fuel II                                                                       Treat Rate (ppm)                                                                      0   50 75  100 125 150 175 200                                        __________________________________________________________________________      Formulation X -3 -7  -12 (A) -16 (A) -16 -18 -18                                -7  -14 (A) -16 (A) -17 -18 -18                                                  -7 -15 -13  -16                                                               -8 -15 (A) -15  -16                                                          -12 (A) -15  -16                                                              -14 (A) -14 (A)  -17                                                          -15 (A) -15                                                                   -16 -17 (A)                                                                   -14 (A) -14 (A)                                                               -13 (A)                                                                       -13 (A)                                                                       -14 (A)                                                                   Formulation Y -3   -16 -17                                                        -16 -18                                                                       -15 (A) -17                                                                   -16 -16                                                                       -14 -15                                                                       -12 -16                                                                       -16 -17                                                                       -16 -15                                                                 __________________________________________________________________________     N.B. (A) indicates irregularity in the aspiration time curve, i.e. a plot     of time to fill the CFPP pipette vs. temperature, indicating an aspiratio     anomaly.                                                                 

The results show that fuels containing formulation Y of the inventionbecame free of aspirations at a much lower treat rate than fuelscontaining comparison formulation X. For example, in Fuel I aspirationsare absent with Formulation Y at 150 ppm whilst with the comparativeethylene-vinyl acetate bipolymer formulation X, 225 ppm was required toprovide a fuel composition giving reliable aspiration free results.

We claim:
 1. A fuel composition meeting its CFPP specification andhaving a reduced tendency for aspiration comprising:(A) a majorproportion of a middle distillate petroleum fuel having a wax content ofless than 2 wt % at 10° C. below the wax appearancee point of the fuel,and either(i) a final boiling point of greater than 355° C. and either a(90-20%) distillation range of greater than 115° C. or a (FBP-90)distillation range of 30° C. or greater; or (ii) a final boiling pointof greater than 360° C., and either a (90-20%) distillation range ofgreater than 110° C. or a (FBP-90%) distillation range of 25° C. orgreater; or (iii) a final boiling point of greater than 370° C. andeither a (90-20%) distillation range of greater than 100° C. or a(FBP-90%) distillation range of 25° C. or greater, all temperaturesbeing measured in accordance with ASTM D-86, and (B) a minor proportionof an additive comprising(B1) an ethylene-unsaturated ester copolymerflow improver wherein said ethylene-unsaturated ester copolymercomprises an ethylene copolymer having, in addition to units derviedfrom ethylene, units of the forumla:

    --CR.sup.5 R.sup.6 --CHR.sup.7 --

wherein R⁶ represents hydrogen or a methyl group; R⁵ represents a--OCOCR⁸ or --COOR⁸ group wherein R⁸ represents hydrogen or a C₅ or C₂₈,straight or branched chain alkyl group; and R⁷ represents hydrogen or a--COOR⁸ or --OCOR⁸ group, the flow improver having an unsaturated estercontent of 10 mole % or greater; and, optionally (B2) anethylene-unsaturated ester copolymer that is different from (B1).
 2. Thecomposition of claim 1, wherein (B1) has an unsaturated ester content of11 to 20 mole %.
 3. The composition of claim 1 further comprising atleast one additive selected from the group consisting of: detergents,antioxidants, corrosion inhibitors, dehazers, demulsifiers, metaldeactivators, antifoaming agents, cetane improvers, cosolvents, packagecompatibilisers, reodorants, lubricity additives and antistaticadditives.
 4. The composition of claim 1 wherein saidethylene-unsaturated ester copolymer has a polymethylene backbonedivided into segments by hydrocarbyl side chains interrupted by one ormore oxygen atoms and/or carbonyl groups.
 5. A fuel composition meetingits CFPP specification and having a reduced tendency for aspirationcomprising:(A) a middle distillate petroleum fuel having a wax contentof less than 2 wt % at 10° C. below the wax appearance point of thefuel, and either(i) a final boiling point of greater than 355° C. andeither a (90-20%) distillation range of greater than 115° C. or a(FBP-90%) distillation range of 30° C. or greater; or (ii) a finalboiling point of greater than 360° C., and either a (90-20%)distillation range of greater than 110° C. or a (FBP-90%) distillationrange of 25° C. or greater; or (iii) a final boiling point of greaterthan 370° C.; and either a (90-20%) distillation range of greater than100° C. or a (FBP-90%) distillation range of 25° C. or greater, alltemperatures being measured in accordance with ASTM D-86, and (B) about1 to 5000 ppm (active ingredient) by weight per weight of petroleum fuelof an additive comprising (B1) an ethylene-unsaturated ester copolymerflow improver wherein said ethylene-unsaturated ester copolymercomprises an ethylene copolymer having, in addition to units derivedfrom ethylene, units of the formula:

    --CR.sup.5 R.sup.6 --CHR.sup.7 --

wherein R⁶ represents hydrogen or a methyl group; R⁵ represents a--OCOCR⁸ or --COOR⁸ group wherein R⁸ represents hydrogen or a C₅ or C₂₈,straight or branched chain alkyl group; and R⁷ represents hydrogen or a--COOR⁸ or --OCOR⁸ group, the flow improver having an unsaturated estercontent of 10 to 25 mole % or greater; and optionally (B2) anethylene-unsaturated ester copolymer that is different from (B1),wherein(B1) and (B2) copolymer each comprises an ethylene copolymer having, inaddition to units derived from ethylene, units of the formula:

    --CR.sup.5 R.sup.6 --CHR.sup.7 --

wherein R⁶ represents hydrogen or a methyl group; R⁵ represents a--OOCR⁸ or --COOR⁸ group wherein R⁸ represents hydrogen or a C₁ or C₂₈,straight or branched chain alkyl group; and R⁷ represents hydrogen or a--COOR⁸ or --OOCR⁸ group.
 6. The composition of claim 1 wherein saidethylene-unsaturated ester copolymer of (B1) comprises between about 10to 25 mole % of said unsaturated ester.
 7. The composition of claim 1wherein said ethylene-unsaturated ester copolymer has a number averagemolecular weight, as measured by vapor phase osmometry, in the rangebetween about 1,000 to 10,000.
 8. The composition of claim 1 whereinsaid ethylene-unsaturated ester copolymer has 15 or fewer methylterminating side branches per 100 methylene groups, as measured bynuclear magnetic resonance, other than methyl groups on a comonomerester and other than terminal methyl groups.
 9. The composition of claim1 wherein said ethylene-unsaturated ester copolymer has a polydispersityof between about 1 to 6, said polydispersity being the ratio of weightaverage molecular weight to number average molecular weight both asmeasured by Gel Permeation Chromatography using polystyrene standards.10. The composition of claim 1 wherein said ethylene-unsaturated estercopolymer of (B2) comprises an ethylene copolymer having, in addition tounits derived from ethylene, units of the formula:

    --CR.sup.5 R.sup.6 --CHR.sup.7 --

wherein R⁶ represents hydrogen or a methyl group; R⁵ represents a--OOCR⁸ or --COOR⁸ group wherein R⁸ represents hydrogen or a C₁ to C₂₈,straight or branched chain alkyl group; and R⁷ represents hydrogen or a--COOR⁸ or --OOCR⁸ group.
 11. The composition of claim 1 wherein saidethylene-unsaturated ester copolymer of (B2) is an ethylene-vinylacetate bipolymer.
 12. The composition of claim 1 wherein saidethylene-unsaturated ester copolymer of (B2) comprises an ethylenecopolymer having more than one polymer, one polymer having anunsaturated ester content of between about 10 to 25 mole % and anotherpolymer having an unsaturated ester content of less than 10 mole %. 13.The composition of claim 1 further comprising a comb polymer whichconsists of molecules in which long chain branches such as hydrocarbylbranches, optionally interrupted with one or more oxygen atoms and/orcarbonyl groups, having from about 6 to 30 carbon atoms, arc pendantfrom a polymer backbone, said branches being bonded directly orindirectly to said backbone.
 14. The composition of claim 1 furthercomprising a linear compound comprising at least one substantiallylinear alkyl group having between about 10 to 30 carbon atoms isconnected via an optional linking group that may be branched to anon-polymeric residue to provide at least one linear chain of atoms thatincludes the carbon atoms of said alkyl groups and one or morenon-terminal oxygen, sulfur and/or nitrogen atoms.
 15. The compositionof claim 1 further comprising a polar compound which comprises anoil-soluble polar nitrogen compound carrying one or more hydrocarbylsubstituted amino or imino substituents, said hydrocarbyl group(s) beingmonovalent and containing 8 to 40 carbon atoms.
 16. The composition ofclaim 1 wherein said fuel oil is selected from the group consisting of:kerosene, jet fuels, diesel fuels, heating oils, and heavy fuel oils.17. The composition of claim 1 wherein said additive is added to saidmiddle distillate petroleum-based fuel oil in the range between about 1to 5,000 ppm.